Techniques for probabilistic weighting of single word terms date back to at least 1976 in the landmark publication by [[Stephen Robertson (computer scientist)|Stephen E. Robertson]] and [[Karen Spärck Jones]].<ref>{{citeCite doijournal | doi = 10.1002/asi.4630270302| title = Relevance weighting of search terms| journal = Journal of the American Society for Information Science| volume = 27| issue = 3| pages = 129| year = 1976| last1 = Robertson | first1 = S. E. | authorlink1 = Stephen Robertson (computer scientist)| last2 = Spärck Jones | first2 = K. | authorlink2 = Karen Spärck Jones}}</ref> Robertson stated that the assumption of word independence is not justified and exists as a matter of mathematical convenience. His objection to the term independence is not a new idea, dating back to at least 1964 when H. H. Williams stated that "[t]he assumption of independence of words in a document is usually made as a matter of mathematical convenience".<ref>{{cite journal|last=WILLIAMS |first=J.H. |title=Results of classifying documents with multiple discriminant functions |url=http://oai.dtic.mil/oai/oai?verb=getRecord&metadataPrefix=html&identifier=AD0612272 |journal= Statistical Association Methods for Mechanized Documentation, National Bureau of Standards |___location=Washington |pp=217-224 |year=1965}}</ref>
In 2004, Anna Lynn Patterson filed patents on "phrase-based searching in an information retrieval system"<ref>{{patent|US|20060031195}}</ref> to which [[Google]] subsequently acquired the rights.<ref>[http://www.seobythesea.com/2012/02/google-acquires-cuil-patent-applications/ Google Acquires Cuil Patent Applications]</ref>
